For producing polycarbonates, known are a process of directly reacting an aromatic dihydroxy compound such as bisphenol A with phosgene (interfacial polycondensation), a process of transesterifying an aromatic dihydroxy compound such as bisphenol A with a carbonic diester such as diphenyl carbonate in melt state or solid state (a melt process, a solid state process, respectively) and so forth.
However, in the interfacial polycondensation, there have been problems such as requirement of using toxic phosgene and occurrence of corrosion in production apparatus caused by chlorine-containing by-products such as sodium chloride. The conventional transesterifying process needs complicated processes for producing carbonic diester as a raw material. Such a production process including a raw material production process, a recycle process of by-products and so forth in total is less economical.
The solid state process has been attracted as a process of giving products with superior quality and an environmentally friend process since it requires no halogen solvents such as methylene chloride, and it requires a lower polymerization temperature than that of the melt process.
In the solid state process, it has been desired that a prepolymer was produced through a melt process and then modified so as to have the specific property by using a poor solvent such as acetone (JP 3-22330A). However, in this process, it was difficult to control the molecular weight distribution of prepolymer because it was produced by the melt process, therefore, the increase of molecular weight in the solid state polymerization was not enough.
Further proposed is a method in which prepolymer was produced through an oxidative carbonylation reaction and then the molecular weight thereof was increased by transesterification (JP 2000-281769). However, in this method, there have been problems to be solved, such as difficulty of separating and recovering the prepolymer, because the physical property of the prepolymer was not controlled and homogeneous catalyst was used.